A leg to stand on

A new prosthetic limb design that anchors directly onto the bone provides more comfort and increased mobility - it has just been approved for use in the UK by the FDA. Credit@U.S. Department of Defense Current Photos/Flickr

An innovative prosthetic leg design that anchors directly onto the bone has just been approved by the FDA. The design may change the lives of amputees who find effective use of the traditional ball-and-socket-prosthetics challenging.

Typically, a prosthetic limb may require a cup-shaped socket that is fastened to an amputee’s residual limb. However, some amputees have very little residual limb available to use this type of prosthetic. The Osseoanchored Prosthesis for the Rehabilitation of Amputees (OPRA) design remedied this challenge through the use of fixtures that are attached directly into the person’s bone – to which the artificial limb may be attached.

The technology is attached surgically through two stages. Firstly, a cylindrical component is implanted directly into the bone. To ensure the person’s immune system accepts the fixture without the risk of immunorejection, engineers use titanium. Six months later, a second rod is implanted, which extends through the skin and may be clipped onto a prosthetic. The six month gap between the two procedures allows time for the patient to be trained in its use before being issued a customised prosthetic.

A study carried out in 2014 and published in the journal Physical Medicine and Rehabilitationdemonstrated how the new technology might increase a patient’s manoeuvrability, comfort and function. In addition, the device sits comfortably without the heat and chafing that comes with traditional prosthetics.

The new prosthetic design may be used for legs, arms and hands, however the FDA appears to be only approving its application to adults with leg amputations above the knee. William Maisel, acting director of the Office of Device Evaluation in the FDA’s Center for Devices and Radiological Health, explained that, “The OPRA device may help those with above-the-knee amputations who have had problems with rehabilitation and have been [challenged] to benefit from available socket prostheses.”

A team from University College London (UCL) led by Professor Gordon Blunn, who is head of UCL’s Centre for Biomedical Engineering, solved a challenge surrounding bone-anchored prosthetics by modelling the design on the way deer antlers are attached. Engineers created a device, named the Intraosseous Transcutaneous Amputation Prosthetics (Itaps), which has a honeycomb structure to allow human soft tissue to bridge the connection between skin and bone, reducing the chances of bacteria making their way in.

The Itap design is based on the way deer antlers are attached, using a porous structure to promote the soft tissue to seal the skin-bone gap. Credit@Gilad Rom/Flickr

The effectiveness of the device has been shown in both animals and humans. Famously, Oscar the cat was fitted with similar prosthetic feet (a pioneering operation at the time) after needing both its back paws replaced following an incident. Oscar was the first animal to receive two bionic leg implants. The new paws are custom-made implants that anchor directly onto Oscar’s ankles.

The prosthetic has also been implanted in 20 amputees in a successful 2014 clinical trial. “[My] ability to know where [my foot] is improved dramatically because you [may] feel it through the bone,” Mike O’Leary, an above-the-knee amputee who participated in the trial, said. “A textured road crossing, I [may] feel that. You essentially had [little] sensation with a socket and with Itap you [may] feel everything.” The data from the trial ultimately seemed to prove robust enough for the FDA to allow its deployment in the UK. The US is also taking small steps to approve prosthetic limb designs similar to the Itap for bone-anchored limbs, which may benefit a substantial number of amputees including US Veterans.

What productive qualities might be necessary for the ideal prosthetic limbs?

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